Detection of Mycobacterium species in clinical species is important as a clinical diagnostic tool. Historically, M. tuberculosis was thought to be the only clinically significant pathogen in this genus. A rise in the incidence of drug-resistant strains of M. tuberculosis has further emphasized the need to detect this species. Other Mycobacterium species, however, are also clinically important. These are sometimes referred to as “MOTT” for Mycobacterium other than tuberculosis, commonly including M. avium/intracellulare complex organisms (M. avium, M. intracellulare, M. paratuberculosis, commonly referred to as MAIC), M. gordonae, M. fortuitum, M. chelonae, M. mucogenicum and mixtures of Mycobacterium species in a clinical specimen. For example, fast-growing opportunistic infections by M. avium complex (MAC) bacteria have been shown to occur frequently in AIDS and other immunocompromised individuals. In such infected individuals, at least 106 MAC cells/ml of sputum sediment have been found. Therefore, detection assays that can detect, and optimally distinguish between, many species of Mycobacterium are clinically important.
Many clinical methods for detecting and identifying Mycobacterium species in samples require analysis of the bacteria's physical characteristics (e.g., acid-fast staining and microscopic detection of bacilli), physiological characteristics (e.g., growth on defined media) or biochemical characteristics (e.g., membrane lipid composition). These methods require relatively high concentrations of bacteria in the sample to be detected, may be subjective depending on the clinical technician's experience and expertise, and are time-consuming. Because Mycobacterium species are often difficult to grow in vitro and may take several weeks to reach a useful density in culture, these methods can also result in delayed patient treatment and costs associated with isolating an infected individual until the diagnosis is completed. More recently, assays that detect the presence of nucleic acid derived from bacteria in the sample have been preferred because of the sensitivity and relative speed of the assays. In particular, assays that use in vitro nucleic acid amplification of nucleic acids present in a clinical sample can provide increased sensitivity and specificity of detection. Such assays, however, can be limited to detecting one or a few Mycobacterium species depending on the sequences amplified and/or detected.
Assays and reagents for detecting Mycobacterium nucleic acid sequences have been previously disclosed, for example, in U.S. Pat. Nos. 5,554,516, 5,766,849, 5,795,752, 5,906,917, 5,908,744; European Patent Nos. EP 0528306 and EP 0818465; and published PCT Patent Applications WO 9636733 and WO 9723618.
The present invention provides compositions and relatively simple diagnostic methods that detect a wide spectrum of Mycobacterium species that may be present in a clinical sample.